The present invention relates generally to clutches, and particularly to motor vehicles clutches, and deals more specifically with that part of a clutch, commonly called the cover assembly, which forming a unit in itself, is attached to the reaction plate after the insertion of a friction disc.
Generally speaking such a cover assembly comprises a first annular part known as the cover, a second annular part known as the pressure plate associated in rotation with the cover by coupling means permitting an axial movement of said pressure plate relative to said cover, and between the cover and the pressure plate, axially acting resilient means urging the pressure plate in a direction away from the cover.
Dealing e.g., with a mechanism for a diaphragm clutch, the resilient means are constituted by the peripheral part, forming a Belleville washer, of a third annular part known as the diaphragm, the central portion of which is fragmented into radial fingers for actuation by the clutch release mechanism, the radial fingers controlling the pivoting of the diaphragm within the assembly, and the diaphragm bearing upon the pressure plate by its peripheral portion.
As is well known, a clutch is intended to be inserted between a driving shaft and a driven shaft. In a motor vehicle, the driving shaft is constituted by the engine output shaft and the driven shaft by the input shaft of the gearbox.
In the case of an in-line assembly of the engine and gearbox, the location of the gearbox is often inaccessible, particularly when the engine is arranged transversely of the vehicle; furthermore, it is a requirement that the axial dimension of the clutch, and hence of its mechanism, must be the smallest possible.
Now hitherto, the axial dimension of a clutch cover assembly depends upon the state, free or under load, of the axially acting resilient means interposed between the cover and the pressure plate.
This is the case especially where, as mentioned hereinbefore, the resilient means comprise the peripheral portion of a diaphragm.
In this case, when the pressure plate moves axially away from the cover, the central portion of the diaphragm which is fragmented into radial fingers moves away simultaneously from the pressure plate in a sense of movement which is axially opposite to that of the pressure plate; when the clutch mechanism concerned is in the free state, i.e., prior to assembly when it is not fitted to the reaction plate, this central portion projects axially beyond the cover, through the central aperture thereof, and it is the edge of this aperture which limits its projection, the central portion bearing against this edge.
It is only in the position of maximum clearance of the clutch, when the peripheral portion forming a Belleville washer of the diaphragm is under load, (i.e. when the cover assembly is bolted to the reaction plate), that the central portion of the diaphragm occupies a minimum axial space, for which it can be completely contained in the overall volume of the cover.
Now, it is desirable that the dismantling and removal of a clutch cover assembly, necessary for its replacement or for its repair, should be performed radially, and impose only a limited action of withdrawal or of dismantling on the various other elements involved.
It is easy to understand that, for such a radial withdrawal of the clutch assembly, any axial projection of the central portion of the diaphragm from the cover is likely to make such a withdrawal more difficult, or even impossible without necessitating a general dismantling of the gearbox and/or of the engine, if the space actually available for this withdrawal is no more than the axial dimension of the cover alone.
Now, on any assumption, such a projection inevitably occurs as soon as the assembly is detached from the reaction plate.
Inversely, the repositioning of this cover assembly, or the positioning of a new assembly in substitution therefor, is difficult, if not impossible, to perform radially under the conditions of reduced free axial dimension stipulated hereinbefore, and for the same reasons as those explained.
In French Pat. No. 882,854, which concerns a clutch in which the resilient means to which the pressure plate is subjected are formed by helicoidal springs acting axially between the cover and said pressure plate, (and not by the peripheral portion of a diaphragm), it was proposed to use a retaining wedge adapted to maintain the pressure plate axially in relation to the cover, against the action of the resilient means.
The retaining wedge proposed for this purpose must however be inserted between the cover and the head of a rivet which, being integral with the pressure plate, extends axially through the cover.
It is therefore only suitable for clutch cover assemblies provided with rivets; it is not suitable for assemblies which do not use rivets.
It is an object of the present invention to provide an arrangement which, by permitting a direct action of a retaining shim between the pressure plate and the cover, enables this difficulty to be overcome and which at the same time present other advantages.